<!DOCTYPE html>
<html lang="zh-CN">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <button>按钮一</button>
    <button>按钮二</button>
    <button>按钮三</button>
    <button>按钮四</button>
    <button>按钮五</button>
    <script>
        let btns = document.querySelectorAll("button")
        for (let i = 0; i < btns.length; i++) {
            btns[i].onclick = function () {
                alert(i)
            }
        }
    </script>
</body>

</html>